Pipette devices are used in a multitude of industries for the transfer of liquids to conduct experimental analysis. As such, to provide control within the experiments being performed, disposable pipette tips are used and intended for one-time use. Disposable pipette tips are employed with both manual pipette devices and automated pipette devices having a large number of pipette units arranged in a row or in a matrix for aspirating samples simultaneously from a large number of vessels and dispensing them elsewhere.
Disposable pipette tips have been constructed historically to interface to either a conical or stepped coupling stud. In the cases where a conical coupling stud is used, the disposable tip is constructed in a manner that it must be pre-stressed onto the coupling stud to provide an air tight seal. Due to the tolerances of the two interfacing components, the distance to the end of the tip that comes in contact with liquid is not well controlled. In addition, high press forces are required to pre-stress the tip to create the air tight seal. As a result, microfissures may be formed in the pipette tip which are a cause of leakage. Moreover, the high press forces upon placement of the pipette tip have the disadvantage that for the release of the pipette tip correspondingly high forces have to be applied.
The assignee of the present application, HAMILTON Company, teaches in U.S. Pat. No. 7,033,543, issued Apr. 25, 2006, a stepped coupling stud in conjunction with an O-ring that provides a solution for reducing the high press force required to create an air tight seal as well as providing well defined axial positioning of the end of the tip that comes in contact with liquid. As the O-ring is compressed, it provides an axially directed force to not only provide the air-tight seal, but to engage an axial coupling feature on the coupling stud to a counter axial coupling feature on the tip.
Notwithstanding, current systems utilizing a stepped coupling stud and a solitary O-ring configuration are problematic when the O-ring becomes compromised because the result is an impairment in the air-tight seal and the performance of the pipette device.
Additionally, the compression of the O-ring results in the deformation of the O-ring which in turn provides the axially directed force and air-tight seal against the working surface of the pipette tip. Counter to this operation, when the compression of the O-ring is removed, the O-ring must disengage from the working surface of the pipette tip to allow the pipette tip to be removed from the coupling stud and the pipette device for disposal. If the O-ring does not fully decompress, some residual force will remain resulting in keeping the tip engaged to the coupling stud and thus requiring an automated external axial counterforce to remove the tip for disposal.
Moreover, as the size of the holes to and/or from which liquid is transferred decreases, the need for precision positioning of all of the tips in a controlled manner increases in order to allow successful targeting.
Hence, there is a need to ameliorate or overcome one or more of the significant shortcomings delineated hereinabove.